Magnetic recording medium and method of making the same

Abstract

A magnetic recording medium, and a method of making the same, including an irreversible recording layer which undergoes an irreversible change of saturation magnetization upon heating. The magnetic recording medium includes on at least a portion of a substrate an irreversible recording layer which contains an irreversible recording material undergoing an irreversible change of saturation magnetization upon heating. The irreversible recording layer includes at least in part a fixed information recording region for recording the fixed information of the medium. In the fixed information recording region, a plurality of heated bars whose saturation magnetization has been irreversibly changed are arrayed substantially parallel to each other. The array pattern of the heated bars or the array pattern of unheated bars disposed between adjacent ones of the heated bars contains the fixed information encoded in a frequency modulation process or phase modulation process.

What is claimed is: 
     
       1. A magnetic recording medium comprising: a substrate; and   an irreversible recording layer supported by said substrate and including an irreversible recording material capable of undergoing an irreversible change of saturation magnetization upon heating,   the irreversible recording layer having a fixed information recording region comprising an array pattern of a plurality of heated bars and unheated bars,   the heated bars having an irreversibly changed saturation magnetization and being substantially parallel to each other,   the unheated bars being disposed between adjacent heated bars, and   the array pattern corresponding to the fixed information encoded by means of one of a frequency modulation process and a phrase modulation process.   
     
     
       2. A magnetic recording medium as set forth in claim 1, wherein said fixed information corresponds to a member of the group consisting of value information and marker information. 
     
     
       3. A magnetic recording medium as set forth in claim 1, further comprising a magnetic recording layer between said irreversible recording layer and said substrate. 
     
     
       4. A magnetic recording medium as set forth in claim 3, wherein said irreversible recording layer includes a soft magnetic material in addition to the irreversible recording material. 
     
     
       5. A magnetic recording medium as set forth in claim 3, wherein said irreversible recording layer is comprised of a soft magnetic material layer including said soft magnetic material and an irreversible recording material layer including said irreversible recording material. 
     
     
       6. A magnetic recording medium as set forth in claim 1, wherein said irreversible recording layer includes a hard magnetic material whose saturation magnetization does not substantially change upon heating and which has a higher coercivity than said irreversible recording material. 
     
     
       7. A magnetic recording medium as set forth in claim 6, wherein said irreversible recording layer is comprised of an irreversible recording material layer including said irreversible recording material and a hard magnetic material layer including said hard magnetic material. 
     
     
       8. A magnetic recording medium as set forth in claim 6, wherein said hard magnetic material has a coercivity of at least 300 Oe. 
     
     
       9. A magnetic recording medium as set forth in claim 1, wherein said irreversible recording layer has at least one recording track comprising: at least two track elements in which heated bars are arrayed in a bar code array, said at least two track elements being arranged substantially parallel to each other; and   an asymmetric region in which the array pattern of heated bars differs between at least two track elements.   
     
     
       10. A magnetic recording medium as set forth in claim 1, wherein said irreversible recording layer has a surface roughness of up to 1 μm. 
     
     
       11. A magnetic recording medium as set forth in claim 7, wherein said hard magnetic material has a coercivity of at least 300 Oe. 
     
     
       12. A method of making a magnetic recording medium comprising the steps of: forming an irreversible recording layer supported by a substrate and including an irreversible recording material capable of undergoing an irreversible change of saturation magnetization upon heating,   heating the irreversible recording layer such that a plurality of heated bars whose saturation magnetization has been irreversibly changed are arrayed substantially parallel to each other,   wherein the heating step is performed so as to form an array pattern of a plurality of members from the group consisting of the heated bars and unheated bars disposed between adjacent heated bars, said array pattern corresponding to recorded information coded using one of a frequency modulation process and a phase modulation process.   
     
     
       13. A method of making a magnetic recording medium as set forth in claim 11 wherein the heating step is performed by scanning with a heating element in a scanning direction substantially perpendicular to a direction in which the irreversible recording layer is scanned with a read head during a reading operation. 
     
     
       14. A method of making a magnetic recording medium as set forth in claim 12, comprising: controlling the heating step so as to provide at least two track elements in which heated bars are arrayed in a bar code array, said at least two track elements being arranged substantially parallel to each other to construct one recording track, and the recording track including at least in part an asymmetric region in which the array pattern of heated bars differs between at least two track elements.   
     
     
       15. A method of reading a magnetic recording medium having a layer including a hard magnetic material and an irreversible recording material, said layer having unheated bars and heated bars with irreversibly changed saturation magnetization and arrayed in a bar code pattern corresponding to fixed information encoded by a process of the group consisting of a frequency modulation process and a phase modulation process, said method of reading comprising the steps of: magnetizing the hard magnetic material in a hard magnetic direction;   detecting a magnetization change of said irreversible recording layer; and   applying a biasing magnetic field in an orientation opposite to said hard magnetizing direction and at a level that does not cause said hard magnetic material to reverse its magnetization.   
     
     
       16. A method of reading a magnetic recording medium as set forth in claim 15, wherein the level of the biasing magnetic field is lower than a coercivity of said hard magnetic material and higher than a coercivity of said irreversible recording material. 
     
     
       17. A method of reading a magnetic recording medium having a layer including a hard magnetic material and an irreversible recording material, said layer having unheated bars and heated bars with irreversibly changed saturation magnetization and arrayed in a bar code pattern corresponding to fixed information encoded by a process of the group consisting of a frequency modulation process and a phase modulation process, said method of reading comprising the steps of: magnetizing the hard magnetic material in a hard magnetic direction;   detecting a magnetization change of said irreversible recording layer; and   applying a biasing magnetic field in said hard magnetizing direction.   
     
     
       18. A method of reading a magnetic recording medium as set forth in claim 17, wherein a level of the biasing magnetic field is lower than a coercivity of said hard magnetic material and higher than a coercivity of said irreversible recording material.